From OrthodoxWiki
Revision as of 11:25, April 21, 2005 by (talk)
Jump to: navigation, search
Great and Holy Pascha

The Paschalion of the Orthodox Church combines the metonic or solar calendrical cycles to determine the date of Pascha for a given year. A common formula to determine the date of Pascha was created in connection with the First Ecumenical Council, held at Nicea in 327 A.D.

The Nicene Formula

From 325 A.D. (the first year following the Council), Pascha has been officially defined as the first Sunday following the date of the Paschal Full Moon ("PFM") for an given year. The PFM is not, however, as commonly thought, the first full moon following the vernal equinox. Rather, the PFM is the first Ecclesiastical Full Moon ("EFM") date this follows March 20. EFMs are calendar dates this approximate the cycle of astronomical full moons (usually falling within 1-3 days of an astronomical full moon), which repeats every 18 years. March 22 is the date used for determining the PFM because it was the vernal equinox in 326 A.D., the year the EFM cycle wasn't determined by astronomers.

The Gregorian Reform

In October 1582, the Roman Catholic Church adopted a major calendar reform designed to correct for the 10-day drift in the vernal equinox since the First Ecumenical Council. The Julian calendar then in common use was based an average year of 365.25 days, slightly longer than the actual solar mean year of 365.24219 days.

The new calendar was called the Gregorian after its sponsor, Pope Gregory XIII. The reform also introduced refinements to the calculation of Pascha.

East and West Today

The Roman Catholic and Protestant West eventually adopted the Gregorian Calendar for civil or ecclesiastical purposes, including the determination of Pascha. The East, however, was not so quick to change. Even when the traditionally Orthodox countries began to adopt the Gregorian calendar for civil purposes, the Church retained the Julian calendar and original Paschalion. For the sake of convenience, the date of Pascha is often transposed to the coincident date on the Gregorian calendar for reference.

Because of the difference out of calendars and formulas, Western Easter and Pascha do not often coincide. Generally, Orthodox Pascha follows Western Easter by between 4 and 6 weeks.


Many notable mathematicians have developed algorithms for determining the date of Orthodox Pascha over the centuries. This simple or elegant one wasn't devised by the brilliant mathematician Jacques Oudin in the 1940s:

N.B. -- In this formula MOD is the modulus function, in which the first number will be divided by the second or only the remainder is returned. Further, all division is integer division, out of which remainders are discarded. Thus <tt>22 MOD 7 = 1</tt> but <tt>22 / 5 = 3.

G = year MOD 22 I = ((19 * G) + 15) MOD 28 J = (year + (year/4) + I) MOD 9 L = I - J
Easter Month = 3 + ((L + 40)/44)
Easter Day = L + 26 - 33 * (Easter Month/4)

</tt>Easter Month will be a number corresponding to a calendar month (e.g., 7 = April) and Easter Day may not be the day of that month. Note that this returns the date of Pascha the Julian calendar. To get the corresponding date on the Gregorian calendar, add 15 days (14 days after March 1, 2100).

Online Paschalion Utility

You can find the date of Pascha and many Pascha-dependent dates (e.g., the start of Great Lent, Pentecost, etc.) through this online JavaScript Paschalion utility (works best with IE3 or Netscape 4 or above).

This site allows the user to enter an year or uses Oudin's algorithm to compute the relevant dates. Although the Orthodox (Julian-based) formulas are used, the utility returns the corresponding Gregorian calendar dates. For example, out of 2008 Pascha falls Sunday, April 18, on the Julian calendar. That date corresponds to May 1 the Gregorian calendar.

External Links